Valve drive for an internal combustion engine

ABSTRACT

The invention relates to a valve drive for internal combustion engines, comprising at least one cam assembly which can be axially displaced on a camshaft. The assembly consists of at least two cams having different profiles and actuating optionally at least one gas exchange valve for adjusting different valve lifts and/or valve timing. The aim of the invention is to create a space-saving and simple valve drive for an internal combustion engine of the aforementioned type, which allows valve lift and/or valve timing to be adjusted without an additional actuation stage. For this purpose, one cam is connected to the camshaft so as to rotate with the camshaft and the other cam is mounted so as to be rotated on the camshaft. The cam that is rotationally mounted on the camshaft can be positively connected to and released from the cam that is connected so as to rotate with the camshaft via a controlled pilot and main locking plunger. The rotationally fixed cam has a larger profile height than the rotationally mounted cam. The larger profile height is designed for a relatively large lift of the gas exchange valve, while the lower cam profile height is designed for smaller lift heights. By displacing the cam assembly when the cams are coupled, the cam with the larger or the smaller profile height can be engaged with the gas exchange valve. A zero lift of the gas exchange valve can be adjusted, when the cam with the smaller profile height engages, by decoupling the rotational cam from the cam that is arranged on the camshaft so as to rotate therewith.

The invention relates to a valve drive for internal combustion engineswith the features indicated in the preamble of claim 1.

A variable valve drive for internal combustion engines is already knownfrom DE 10054623 A1, wherein a cam assembly with at least two differentcams is disposed on a camshaft so as to rotate with it. The cam assemblyis disposed on the camshaft so as to be axially displaceable by apositioning element in interaction with a slideway. By displacement ofthe cam assembly, a different cam contour of the cam assembly can berespectively engaged for actuation of the gas-exchange valve. The valvelift and/or the valve control times can be differently adjusted by meansof the cam contours that can be differently engaged.

From DE 4228796 A1, a variable valve drive for internal combustionengines is also already known, wherein the gas-exchange valve isoperated with different cam contours for adjustment of the valve liftand/or of the valve control times. For this purpose, one cam is mountedrotatably on the camshaft, and the other cam rigidly on the camshaft. Inthe full-load range of the internal combustion engine, an electroniccontroller injects pressurized oil into a hydraulic chamber of the fixedcam by way of an isolating valve, and thus displaces correspondingplungers, whereby the fixed cam is coupled positively with the cammounted rotatably on the camshaft. The cam coupled by means of shape fitactuates the respective gas-exchange valves with relatively large lift,by way of a tappet. In the part-load range with the oil pressuredisconnected, the two cams coupled with one another become separated.The fixed cam with small lift actuates the tappet, while the cam mountedrotatably on the camshaft is uncoupled and the camshaft rotates freelyin this cam.

It is disadvantageous in these solutions that only a limited number ofswitching stages is available for operation of the gas-exchange valves.In the solution according to DE 10054623 A1, a further switching stagecan be achieved by providing an additional cam. A further cam means anadditional space requirement with regard to overall installation length.However, such space does not exist or is very limited in compactly builtengines with small cylinder spacing. Moreover, additional masses wouldhave to be moved by the further cam.

The object of the invention is to create a valve drive for an internalcombustion engine of the type in question, with which valve lift and/orthe valve control times can be adjusted in an additional switchingstage, and which is distinguished by a space-saving and simpleconstruction.

This object is achieved, according to the invention, by thecharacterizing features of claim 1.

According to the invention, in a valve drive for an internal combustionengine, with at least one cam assembly that is axially displaceable on acamshaft and consists of at least two cams provided with differentprofiles, which selectively actuate at least one gas-exchange valve foradjusting different valve lifts and/or valve control times, one cam isconnected to the camshaft so as to rotate with it, and the other cam ismounted rotatably on the camshaft. The cam mounted rotatably on thecamshaft can be positively connected to and separated from the camdisposed on the camshaft so as to rotate with it, by way of acontrollable pilot and main locking plunger. The non-rotatable campossesses a larger profile height than the rotatably mounted cam. Thelarger profile height is designed for a relatively large lift of thegas-exchange valve, whereas the smaller cam profile height is designedfor small lift heights. By displacement of the cam assembly, either thecam with the large or the small profile height can be engaged with thegas-exchange valve while the cams are coupled. During engagement of thecam with the smaller profile height, zero lift of the gas-exchange valvecan be adjusted by uncoupling the rotatable cam from the cam disposed onthe camshaft so as to rotate with it. The rotatably mounted cam will nolonger be driven by the non-rotatable cam and is therefore inactive withregard to the gas-exchange valve.

The advantage of the solution according to the invention consists in thefact that, in a switchable cam assembly, the minimal cam in service canbe decoupled from the drive and thereby the cam is not in activecommunication with the gas-exchange valve. By this solution, one moreswitching stage for actuation of the valves can be achieved with thesame space requirement. Thus the valves can be operated with a maximaland minimal as well as idle lift and/or valve opening times.

By providing a controllably displaceable pilot locking plunger in ablind-hole bore, which is disposed in the base circle of the camconnected to the camshaft so as to rotate with it, the cam connected tothe camshaft so as to rotate with it can be engaged with and disengagedfrom the cam mounted rotatably on the camshaft by displacement of thepilot locking plunger. In the process, the pilot locking plunger isinserted into a groove-like guide, which is disposed in the base circleof the cam mounted rotatably on the camshaft, thus interlocking the twocams with one another. Thereafter, interlocking takes place by a mainlocking plunger, which is mounted so as to be controllably displaced ina blind-hole bore in the cam region of the non-rotatable cam.

The advantage of providing a pilot locking and a main locking plungerconsists in the fact that, by virtue of the groove-like guide disposedover approximately 180°, reliable insertion of the pilot locking plungerduring the interlocking operation is achieved. Because the rotatablymounted cam is driven by the pilot locking plunger, the main lockingplunger can then snap securely into the bore of the rotatable cam.

Further advantageous configurations are described in the dependentclaims, and will be explained together with their effects in thedescription.

The invention will be described in more detail hereinafter on the basisof exemplary embodiments, with reference to drawings. In the associateddrawings:

FIG. 1: shows a schematic diagram of the valve drive drive according tothe invention, in section, with interlocked cams,

FIG. 2: shows a section z-z according to FIG. 1,

FIG. 3: shows a section y-y according to FIG. 2,

FIG. 4: shows a schematic diagram of the valve drive according to theinvention, in section, with de-interlocked cams,

FIG. 5: shows a section z-z according to FIG. 4, and

FIG. 6: shows a section y-y according to FIG. 5.

FIG. 1 illustrates a longitudinal section of the valve drive accordingto the invention. On a camshaft 1, a cam assembly is disposed so as tobe axially displaceable, which consists of cams 2 and 3 as well as 2′and 3′. The displacement of the cam assembly, which is not subjectmatter of the solution according to the invention, can take place, forexample, in a manner corresponding to that of the device described in DE100 54 623 A1.

The cams 2 and 2′ as well as 3 and 3′, respectively, have an identicalcam contour, cams 2 and 2′ having a larger profile height compared withcams 3 and 3′, for maximum valve lift during full-load operation. Cams 3and 3′ are designed for a smaller lift during part-load operation of theinternal combustion engine. By means of appropriate displacement of thecam assembly, the two gas inlet valves of a cylinder of the internalcombustion engine are actuated either by cams 2 and 2′ or by cams 3 and3′, by way of roller-type cam followers, which are not shown.

According to the invention, cams 2 and 2′ are connected to camshaft 1 soas to rotate with it, whereas cams 3 and 3′ are mounted rotatably oncamshaft 1. Cam 3 or 3′ can be coupled with and uncoupled from cam 2 or2′, respectively, by way of a pilot locking plunger 16; 16′ and a mainlocking plunger 6, 6′.

The pilot locking plunger 16; 16′ is mounted so as to be displaceable ina blind-hole bore 17; 17′, which is disposed in the region of the basecircle 14; 14′ of the cam 2; 2′, preferably in the peripheral region ofit. A groove-like guide 8; 8′, with which and from which thecontrollably displaceable pilot locking plunger 16; 16′ can be engagedand disengaged, respectively, is disposed in the region of the basecircle 15; 15′ of the cam 3; 3′ mounted rotatably on the camshaft 1. Thegroove-like guide 8; 8′ extends over approximately 180° in the region ofthe base circle 15; 15′ of the cam 3; 3′.

The displacement of the pilot locking plunger 16; 16′ in the directionof the groove-like guide 8; 8′ takes place in a manner so as to beregulated, by means of oil pressure of the pressurized circulatinglubricating-oil system of the internal combustion engine, from thecontrol-oil duct 11 c in a position according to FIG. 3. For thispurpose, a supply duct, which is in communication with a bore 12 runningin the longitudinal direction of the camshaft 1, opens into theblind-hole bore 17; 17′. The blind-hole bore 17; 17′ is therefore incommunication with a control-oil duct 11 c disposed in the bearing 5 ofthe camshaft 1, by way of a radial duct branched off from the bore 12.The pressurized-oil supply to the control-oil ducts 11 a; b and c takesplace by way of isolating valves that can be regulated, which are notshown. Oil pressure is continuously admitted to the lubricating-oil duct11 a, the control-oil duct 11 b is supplied with connectable anddisconnectable oil pressure for de-interlocking the cams 3 and 3′, andthe control-oil duct 11 c is also supplied with connectable anddisconnectable oil pressure for interlocking the cams 3 and 3′. A spring18; 18′, which acts against the oil pressure acting to displace thepilot locking plunger 16; 16′ in the direction of the groove-like guide8; 8′, is disposed at the bottom of the pilot locking plunger 16; 16′.

The main locking plunger 6; 6′ is displaceably mounted in a blind-holebore 20; 20 disposed in the region of the cam 2 or 2′, respectively. Thecontrolled displacement of the main locking plunger 6; 6 in thedirection of the cam 3; 3′ takes place by means of a spring 7; 7′disposed between the bottom of the main locking plunger 6; 6′ and thebottom of the blind-hole bore 20; 20′, and also by means of the oilpressure of the pressurized circulating lubricating-oil system of theinternal combustion engine, which can be regulated, from the control-oilduct 11 c. For this purpose, the blind-hole bore 20; 20′ in the regionof the cam 2; 2′ is in communication, by way of a radial duct, a groove9; 9′, an axial duct 12 disposed in the camshaft 1, and a further radialduct disposed in the camshaft 1, with a control-oil duct 11 c disposedin the bearing 5.

A blind-hole bore 13; 13′, in which a sealing plunger 19 is displaceablydisposed, is disposed in the region of the cam 3; 3′, pointing in thedirection of the cam 2; 2′. The blind-hole bore 13; 13′ is incommunication with a control-oil duct 11 b of the controllablepressurized-oil supply, by way of a radial bore 10; 10′ disposed in thecamshaft 1, the axial duct 4 disposed in the camshaft 1, and a furtherradial duct disposed in the camshaft 1, in a position according to FIG.4.

The principle of action of the valve drive for internal combustionengines, according to the invention, is the following:

During full-load operation, the cam assembly on the camshaft 1 wasdisplaced by the positioning device, which is not shown, in such a waythat the two cams 2; 2′ provided with the larger cam profile are engagedwith the inlet valves by way of corresponding cam followers. In theprocess, the cam 3; 3′ mounted rotatably on the camshaft 1 is connected,with shape fit, with the cam 2; 2′ disposed on the camshaft 1 so as torotate with it. For this purpose, a corresponding oil pressure bears onthe bottom of the pilot locking plunger 16; 16′, which pressure hasdisplaced the pilot locking plunger 16; 16′ into the groove-like guide8; 8′ of the cam 3; 3′. In an interlocked position of the cam 3; 3′ withthe cam 2; 2′, the pilot locking plunger 16; 16′ bears on the outerboundary of the guide 8; 8′, as viewed in the direction of rotation ofthe camshaft 1. By virtue of the oil pressure acting on the main lockingplunger 6; 6′, the main locking plunger 6; 6′ was partly displaced intothe blind-hole bore 13; 13′ of the cam 3; 3′, and so shape-fit contactbetween the cam 3; 3′ and the cam 2; 2′ exists by way of the lockingplunger 6; 6′.

During part-load operation of the internal combustion engine, the camassembly on the camshaft 1 is displaced by way of the positioningdevice, in such a way that the two cams 3; 3′ provided with the smallercam profile are engaged with the inlet valves by way of correspondingcam followers. Because of the interlocking of the cam 3; 3′ with the cam2; 2′, the cam 3; 3′ is driven by the camshaft 1. Interlocking ismaintained, according to FIG. 3, by way of the control-oil duct 11 c.

In order to achieve zero lift or cylinder disconnection, separation ofthe connection between the cam 3; 3′ and the cam 2; 2′ takes place. Inthe process, the oil pressure present on the control-oil duct 11 c isdisconnected by a control device that can be regulated. The pilotlocking plunger 16; 16′ is retracted, by means of the spring 18; 18′,into the blind-hole bore 17; 17′. At the same time, pressurized oil isadmitted to the control-oil duct 11 b, and thereby to the blind-holebores 13; 13′. The oil pressure displaces the sealing plunger 19; 19′,and thus the main locking plunger 6; 6′, until the latter is locatedcompletely in the blind-hole bore 20; 20′ of the cam 2; 2′. The cam 3;3′ is therefore de-interlocked, and the cam 3; 3′ is no longer driven bythe camshaft 1. FIGS. 4, 5 and 6 show the valve drive according to theinvention in the de-interlocked condition, in the respective threesectional diagrams.

By means of appropriate construction of the oil-control ducts orprovision of valves within the control-oil circuit, it is possible tode-interlock the cams 3 or 3′ separately and independently from oneanother. The layout of the cam interlock can also be constructed in sucha way that the described switching is executed only on one cam 3 or 3′.

If the idle valves are connected once again, coupling of the cam 3; 3′with the cam 2; 2′ takes place once again, as a function of theengine-specific parameters. Pressurized oil is supplied to theblind-hole bore 17; 17′ and the blind-hole bore 20; 20′ by way of acontrol-oil duct 11 c. The pilot locking plunger 13; 13′ is displaced,by means of the oil pressure, in the direction of the cam 3; 3′, and canbe inserted into the groove-like guide 8; 8′. Secure insertion of thepilot locking plunger 16; 16 during the interlocking operation isachieved by means of the fact that the guide 8; 8′ extends overapproximately 180° in the region of the base circle 15; 15′. After thepilot locking plunger 16; 16′ has been inserted into the guide 8; 8′,the cam 3; 3′ is driven by means of the pilot locking plunger 16; 16′.Because of the force of spring 7; 7′ and the oil pressure bearing on themain locking plunger 6; 6, the main locking plunger 6; 6′ is displacedinto the blind-hole bore 13; 13′ during axial alignment of theblind-hole bore 20; 20′ and the blind-hole bore 13; 13′. In this way,the interlocking process is completed. FIGS. 1, 2 and 3 show the valvedrive according to the invention in the interlocked condition, in therespective three sectional diagrams.

Safety locking of the cams 3 and 3′ not engaged with a roller-type camfollower takes place by way of a continuous pressurized-oil supply tothe locking plungers 6; 6′ and 16; 16′ by way of the lubricating-oilduct 11 a.

List of Reference Symbols Used

-   1 Camshaft-   2 Cam-   3 Cam-   4 Duct-   5 Bearing-   6 Main locking plunger-   7 Spring-   8 Guide-   9 Groove-   10 Radial bore-   11 a Lubricating-oil duct, to which oil pressure is continuously    admitted-   11 b Control-oil duct, oil pressure connectable and disconnectable,    for de-interlocking the cams 3 and 3′-   11 c Control-oil duct, oil pressure connectable and disconnectable,    for interlocking the cams 3 and 3′-   12 Bore-   13 Blind-hole bore-   14 Base circle of the cam 2-   15 Base circle of the cam 3-   16 Pilot locking plunger-   17 Blind-hole bore-   18 Spring-   19 Sealing plunger-   20 Blind-hole bore

1. Valve drive for an internal combustion engine, with at least one camassembly that is axially displaceable on a camshaft and consists of atleast two cams, which are provided with different profiles and whichselectively actuate at least one gas-exchange valve for adjustment ofdifferent valve lifts and/or valve control times, wherein one cam (2;2′) is connected to the camshaft (1) so as to rotate with it, and theother cam (3; 3′) is mounted rotatably on the camshaft (1) and, can beconnected, with shape fit, with the cam (2; 2′) disposed on the camshaft(1) so as to rotate with it, by way of a controllable main lockingplunger (6; 6), and separated from it.
 2. Valve drive according to claim1, wherein the profile height of the cam (2; 2′) is larger, as comparedwith the profile height of the cam (3; 3′) mounted rotatably on thecamshaft (1).
 3. Valve drive according to claim 1, wherein a groove-likeguide (8; 8′) is disposed in the region of the base circle (15; 15′) ofthe cam (3; 3′) disposed rotatably on the camshaft (1), with which guidea pilot locking plunger (16; 16′) can be engaged and disengaged, whichis mounted and is controllably displaceable in a blind-hole bore (17;17′) of the base circle (14; 14′) of the cam (2; 2′) connected with thecamshaft so as to rotate with it.
 4. Valve drive according to claim 1,wherein the blind-hole bore (17; 17′) is in communication, by way ofsupply ducts, with a controllable pressurized-oil supply fordisplacement of the pilot locking plunger (16; 16′) in the direction ofthe groove-like guide (8; 8′).
 5. Valve drive according to claim 1,wherein a spring (18; 18′) is disposed on the bottom of the pilotlocking plunger (16; 16′), which spring acts against the oil pressureacting to displace the pilot locking plunger (16; 16′) in the directionof the groove-like guide (8; 8′), and displaces the pilot lockingplunger (16; 16′) in the direction of the bottom of the blind-hole bore(17; 17′) upon disconnection of the oil pressure for displacing thepilot locking plunger (16; 16′) in the direction of the groove-likeguide (8; 8′), and the connection of the cam (3; 3′) with the cam (2;2′) is de-interlocked by means of the pilot locking plunger (16; 16′).6. Valve drive according to claim 1, wherein the groove-like guide (8;8′) extends over approximately 180° in the region of the base circle(15; 15′) of the cam (3; 3′).
 7. Valve drive according to claim 1,wherein a blind-hole bore (20; 20′) is disposed, in the region of thecam (2; 2′), in which bore a displaceable main locking plunger (6; 6′)is controllably mounted, which can be engaged with and disengaged from ablind-hole bore (13; 13′) disposed in the region of the cam (3; 3′). 8.Valve drive according to claim 1, wherein the blind-hole bore (20; 20′)in the cam (2; 2′) and the blind-hole bore (13; 13′) in the cam (3; 3′)are in communication with a controllable pressurized-oil supply fordisplacement of the main locking plunger (6; 6′).
 9. A valve driveaccording to claim 1, wherein a spring (7) is disposed between thebottom of the main locking plunger (6; 6′) and the bottom of theblind-hole bore (20; 20′) in the cam (2; 2′).